In the inside of a case body of an electronic control apparatus loaded onto a vehicle, such as an engine control unit or a control unit for automatic transmission, a great number of heat-generating electronic components, such as processing units and semiconductor elements, are incorporated there, so internal temperature of the case body easily increases.
Accordingly, a radiation structure that heat generated from electronic components is radiated to the outside of a case body of the apparatus from its surface by transmitting the heat to the case body has been developed.
FIG. 8 is an explanatory drawing which shows the above radiation structure. A heat conductive material 104 lies between an electronic component 102 loaded onto a circuit board 101 and a case body 103. Heat generation from the electronic component 102 is transmitted to the case body 103 through the heat conductive material 104, and it is radiated to the outside of the case body 103 from its surface. As the above heat conductive material, a thermal grease has been used.
In case that an adhesive is used as the above heat conductive material, the adhesive becomes rubbery to raise its hardness, thereby rigidly bonding the electronic components to the base portion. For this reason, stress is generated in the electronic components or soldered portions, thereby causing a fear to generate an electrical malfunction.
As compared with the above adhesive, a thermal grease can maintain its viscosity after application, and thereby can restrain concentration of a stress at the electronic components or the soldered portions. (for example, Patent Publication 1)